Mirabegron is chemically described as (R)-2-(2-aminothiazol-4-yl)-4′-[2-[(2-hydroxy-2-phenylethyl)amino]ethyl]-acetanilide or 2-amino-N-[4-[2-[[(2R)-2-hydroxy-2-phenylethyl]amino]ethyl]phenyl]-4-thiazoleacetamide. It has the structure of formula (I).

Mirabegron is an orally active beta-3 adrenoceptor agonist and is under pre-registration in USA and Europe for the potential treatment of urinary frequency, urinary incontinence, or urgency associated with overactive bladder by Astellas Pharma. Mirabegron is approved in Japan. U.S. Pat. No. 6,346,532 B1 discloses mirabegron or a salt thereof and process for its preparation. U.S. Pat. No. 7,342,117 B2 discloses α-form crystal and β-form crystal of mirabegron.
Amorphous forms can be thought of as liquids that have been solidified by the removal of thermal energy or a solvent, in a manner that circumvents crystallization. The amorphous form can have different solubility, stability, and mechanical behavior that can be exploited by pharmaceutical scientists. The solubility of a given solid is a sum of crystal packing energy, cavitation, and solvation energy. Different crystalline forms of a given drug will have different crystal packing energies. The amorphous forms of the same drug require minimal packing energy disruption when dissolving due to absence of an ordered crystal lattice. Thus, the amorphous forms provide the maximal solubility advantage as compared to the crystalline forms of a drug. The ‘apparent solubility’ and dissolution advantage offered by these systems is a vital approach to enhance bioavailability of poorly water soluble drugs.
There always remains a need to provide the new polymorphic forms of mirabegron and processes for making the new polymorphic forms.
The present invention provides amorphous mirabegron and amorphous solid dispersion of mirabegron which can be used in the pharmaceutical composition.
U.S. Pat. No. 7,342,117 B2 discloses the preparation of α-form crystal and β-form crystal of mirabegron.
The methods for the preparation of α-form crystal and β-form crystal of mirabegron as per the literature involves the use of rapid cooling, use of seed material and use of solvents water and ethanol only.
The methods for the preparation of α-form crystal and β-form crystal of mirabegron described in the literature suffer from one or more drawbacks such as reproducibility, use of seed material, less yield, limited solvents, which does not result an industrially feasible process.
Therefore, there is a need to provide simple, reproducible, environment friendly, cost effective, industrially feasible processes for the preparation of α-form crystal and β-form crystal of mirabegron.